B

An excess of residual mercury leaves more γ2 (Sn-Hg) phase in the set amalgam; this phase is electrochemically active and readily undergoes surface oxidation, producing marked tarnish and galvanic corrosion, while actually lowering mechanical strength rather than increasing it [von Fraunhofer 1978, PMID 291078; Ogletree & Marek 1995, PMID 8595831].